The use of wheels utilizing a solid hub with a solid, nonpneumatic tire for applications such as shopping carts, lawn mowers, utility carts, and the like has been common for many years. Such wheels typically comprise a solid hub formed of metal or plastic, and a rubber or plastic tire which is either unitary with the hub, formed as a one piece construction, or formed as a separate part and interconnected to the hub during assembly of the final wheel. In some designs, the hub of the wheel is formed in two halves, which are interconnected prior to attachment of the tire by means of an adhesive, by plastic welding techniques, or by mechanical fasteners, as exemplified by U.S. Pat. No. 2,629,420 to Walklet, U.S. Pat. No. 3,695,728 to Haussels, U.S. Pat. No. 4,153,303 to Tanner, U.S. Pat. No. 4,344,655 to Pellegrine, German Patent No. 2,651,178, and Canadian Patent No. 628,786 (two part assembly without tire). There are also previously known wheel designs in which the tire of the wheel is formed around the hub by molding of the tire onto the outer edge of the hub, exemplified by U.S. Pat. No. 3,387,894 to Louik, U.S. Pat. No. 3,807,474 to Wendt, et. al., U.S. Pat. No. 3,843,202 to Lacerte, U.S. Pat. No. 4,095,846 to Agins, and U.S. Pat. No. 4,592,595 to Freeman.
Each of the different wheel designs known in the prior art suffers from certain distinct disadvantages. Forming of the hub and tire of the wheel as a one piece construction, in which the hub and tire material are the same, requires the use of a sufficiently rigid and non-resilient material to maintain the configuration and structural integrity of the hub of the wheel under load. In that situation, rigidity of the hub is obtained at the expense of the ability of the tire of the wheel to absorb and distribute the shock of impacts upon the tire, which is transmitted without attenuation to the hub, the bearings, and the structure supported by the wheel. Inability to absorb shock can result in accelerated tire wear, accelerated bearing wear, and early hub failure.
Wheel designs in the prior art characterized by unitary hubs and separately attached tires, such as the designs illustrated by U.S. Pat. No. 3,695,728 to Haussels and by German Patent No. 2,651,178, allow the use of a rigid material for the hub of the wheel and more resilient material for the tire, and are more effective in reducing transmission of impact shock through the wheel structure and to the load supported by the wheel. The resiliency of the tire material used in such designs is limited, however, by the need to prevent disengagement of the tire from the hub. As a result, wheels of this design represent a compromise between shock absorbency and maintaining the integrity of the wheel, regardless of whether the tire is separately formed and attached to the hub or molded onto the hub without significant interlock. Those of the prior art wheel designs which utilize a hub formed in sections which are interconnected prior to attachment of the tire suffer the additional disadvantage of hub separation due to failure of the adhesive or other means of interconnection of the hub sections.
In an effort to overcome the problems associated with retention of the tire upon the hub several designs utilizing some system of interlock between tire and hub have been devised. In some such designs the hub and tire are formed in two separate operations and then interconnected in a third discrete operation, as exemplified by U.S. Pat. No. 2,629,420 to Walklet, U.S. Pat. No. 3,387,894 to Louik, and U.S. Pat. No. 4,153,303 to Tanner. While wheels produced in accordance with these designs do provide for somewhat more secure tire retention, the tire remains susceptible to separation from the hub upon impact or the imposition of lateral force, expecially if a tire material sufficiently resilient to provide significant shock absorbing characteristics to the wheel is employed. In other interlock designs, lateral passageways through the hub are formed, and tire material is forced through such passageways during a process of molding the tire onto the hub. Examples of this approach are found in U.S. Pat. No. 3,807,474 to Wendt, et. al., U.S. Pat. No. 3,843,202 to Lacerte, U.S. Pat. No. 4,095,846 to Agins, and U.S. Pat. No. 4,592,595 to Freeman. In each instance, these designs utilize a one piece, rigid hub upon which the tire is formed in a molding process. Wheels produced in accordance with this general design approach have displayed a significant improvement in tire retention as compared to wheels without such interlock features. The use of one piece, rigid hubs has not, however, fully addressed the disadvantages associated with impact shock and transmittal of impact shock through the wheel structure to the wheel bearings and to the structure supported by the wheel.
Thus there continues to be a need in the industry for a method of making a wheel which offers the advantages of a high degree of shock absorbency, strength, physical integrity, and light weight without the disadvantages associated with wheels produced in accordance with the prior art.